Nerve Tissue Flashcards
Nerve Tissue - Composition
Nerve tissue is composed of cells (neurons) that are specialized for conveying information, as well as support cells (called glial cells)
Neurons: Neuron doctrine
Neuron doctrine: released in 1891; stated that individual neurons are the signaling elements of the nervous system
Neurons: How many are there in the human body?
There are over 100 billion neurons in the human body of varying size and shape
Neurons: Function
What is the function of Neurons?
Neurons receive, process, and transmit signals using electrical and chemical mechanisms
Neurons: Function
What do electrical signals typically convey?
Electrical signals typically convey information rapidly from one part of a neuron to another
Neurons: Function
What do chemical signals typically convey?
Chemical signals typically carry information between one part of a neuron and a part of a second neuron or effector cell (muscle cells, glandular cells, and cardiac cells)
Regions of the neuron
Why are neurons structured into regions?
So that organelles can be distributed in a pattern that supports neuronal function
Neuron Regions: Cell body
AKA Perikaryon
Contains the nucleus and surrounding cytoplasm
Does NOT include the cell processes
Neuron Regions: Cell Body - Structure
Nucleus
Large and spherical in shape
Euchromatic (this means that this part of the cell body is pale staining, which indicates that it is active in RNA synthesis) with a prominent nucleolus
Neuron Regions: Cell Body - Structure
Cytoplasm
Abundant rough endoplasmic reticulum (RER and NIssl Substance) and polysomes
Well developed golgi apparatus (post office of the cell)
Numerous mitochondria
Has a well developed cytoskeleton (most distinguishing feature)
Neuron Regions: Cell Body - Function
Trophic (of or retaliating to nutrition) center of the cell
Receptive to stimuli
Neuron Regions: Dendrites
Elongated processes emanating from the cell body
Most neurons have numerous dendrites
Neuron Regions: Dendrites
Structure
Short, tapered, and highly branched
Cytoplasm has organelles similar to the cell body except there are no golgi complexes
Dendritic spines are specializations that are located at some synapses
Neuron Regions: Dendrites
Function
Receptive to Stimuli
Transmit signals towards the cell body
Neuron Regions: Axons
Elongated processes emanating from the cell body
Most Neurons have only one axon
Neuron Regions: Axons
Structure
Long, cylindrical (no tapering), and not highly branched
Cytoplasm has organelles similar to the cell body excet there is no RER or polysomes
Neuron Regions: Axons
Structure - Axon Hillock
Pyramid shaped region where the axon emanates from the cell body
Devoid of Nissl Substance (appears lighter in a stain)
Neuron Regions: Axons
Structure - Terminal Arborization
Branched distal portion of the axon
Neuron Regions: Axons
Function
Generate and conduct signals
Receptive to stimuli
Neuron Regions: Presynaptic Terminal
aka Terminal Bouton or Terminal Bud
Dilated termination of the axon on another cell at the chemical synapse
This region has NO myelin sheath
Neuron Regions: Presynaptic Terminal
Structure - Cytoplasm
Organelles are similar to the cell body except there are more mitochondria and there are small, spherical, membrane bounded synaptic vesicles containing neurotransmitters
Neuron Regions: Presynaptic Terminal
Structure - Active Zones
Regions along the presynaptic membrane concentrated with voltage-gated calcium channels and synaptic vessicles
Neuron Regions: Presynaptic Terminal
Function
Signal transmission to another cell
Neuron Molecular Transport systems
Composition and Function
They are composed of the well developed cytoskeleton of the neuron and are responsible for the transport of substances between the cell body and the axon and its terminals.
They can transport substances at slow (.2 - 4 mm/day), intermediate, and fast (20 - 400 mm/day) speeds
Neuron Molecular Transport systems
Anterograde
Carries material (i.e. organelles, macromolecules) from the cell body to the periphery
Neuron Molecular Transport systems
Retrograde
Carries material (i.e. toxins, viruses) from the periphery to the cell body.
That’s how AIDS travles
Neuron Categories: Motor (Efferent) Neurons
Function
Control effector organs (i.e. muscles, glands)
Neuron Categories (Based on Functional Roles): Motor (Efferent) Neurons
General Somatic Efferent (GSE)
Motor Innervation to skeletal muscles deirved from myotomes
Neuron Categories (Based on Functional Roles): Motor (Efferent) Neurons
General Visceral Efferent (GVE)
Motor innervation to smooth muscle, cardiac muscle, and glands
Neuron Categories (Based on Functional Roles): Motor (Efferent) Neurons
Special Visceral Efferent (SVE)
Motor innervation to skeletal muscles derived from pharyngeal arches
Neuron Categories (Based on Functional Roles): Sensory (Afferent) Neurons
Function
Receive sensory stimuli through specialized nerve endings called receptors
Neuron Categories (Based on Functional Roles): Sensory (Afferent) Neurons
General Somatic Afferent (GSA)
Sensory input from structures associated with the body wall and extremities
Neuron Categories (Based on Functional Roles): Sensory (Afferent) Neurons
General Visceral Afferent (GVA)
Sensory input from the viscera, including smooth muscle, cardiac muscle, and glands
Neuron Categories (Based on Functional Roles): Sensory (Afferent) Neurons
Special Somatic Afferent (SSA)
Sensory input from structures associated with the senses of vision, hearing, and balance
Neuron Categories (Based on Functional Roles): Sensory (Afferent) Neurons
Special Visceral Afferent (SVA)
Sensory input from structures associated with the senses of smell and taste
Neuron Categories (Based on Functional Roles): Interneurons
Connect other neurons
Most numerous
Neuron Categories (Based on Functional Roles): Interneurons
Local
All processes confined in a small area
Neuron Categories (Based on Functional Roles): Interneurons
Projection
Long axons connecting different areas
Neuron Categories (Based on Size and Shape of neuronal Processes): Multipolar
The cell body has multiple dendrites and only one axon
These are the most common.
Motor and interneurons are multipolar
Example: Alphamotor Neurons
Neuron Categories (Based on Size and Shape of neuronal Processes): Bipolar
There is one dendrite and one axon
These neurons are sensory
This is the developmental stage of most neurons
Example: Special sense organs (ie retina, olfactory epithelium, vestibular system, etc.)
Neuron Categories (Based on Size and Shape of neuronal Processes): Pseudounipolar
These neurons have a single process that is close to the cell body and divides into 2 branches: a central and a peripheral axon.
These cells don’t have dendrites.
These neurons are sensory
Example: dorsal root ganglia - The peripheral axon goes from the input to the cell body and the central axon goes form the cell body to the spinal cord
Glial Cells: Overview
How many are there as compared to neurons? What do they look like?
10 times more abundant in the mamillian brain than neurons; they vary greatly in size and shape
Glial Cells: Function
They surround and support the neurons.
They do not participate directly in synaptic interactions and electrical signaling.
Glial Cells: Macroglia
Astrocytes (Types, function, location)
Astrocytes are the most common form of macroglia
Types: Protoplasmic, Fibrous
Function: Structural support, iconic homeostasis, neurotransmitter uptake, repair process, blood brain barrier, secrete growth factors
Location: CNS
Glial Cells: Macroglia
Radial glial astrocytes
Function: Guide migrating neurons and direct outgrowth of axons (help guide axons to their target cells)
Location: Developing CNS
Glial Cells: Macroglia
Oligodendrocytes (Function, Location)
Function: Myelin production - they are capable of myelinating several internodes on several axon in the CNS; oligodendrocytes that do not produce myelin are called SATELLITE CELLS and are associated with neuronal cell bodies.
Location: CNS
Glial Cells: Macroglia
Schwann Cels (Function, Location)
Function: Myelin production - they are capable of myelinateding only one internode on one axon in the PNS Ensheath axons (with or without myelin) Schwann cells that do not ensheath axons are called SATELLITE CELLS and are associated with neuronal cell bodies.
Location: PNS
Glial Cells: Microglia
Function: Macrophagic activity
Location: CNS
Glial Cells: Ependymal cells
Function: Line cavities (cavities are called ventricles)
Location: CNS
**these are sometimes considered epithelial cells
Myelin Sheath: Structure
Segmented, multilamellar, lipid rich, wrapping of axons
Myelin Sheath: Structure
What types of cells form the myelin sheath?
Formed by the plasma membranes of oligodendrocytes in the CNS and Schwann cells in the PNS
Myelin Sheath: Structure
Internode
A single segment of myelin sheath on an axon
Myelin Sheath: Structure
Node of Ranvier
An interval at which the axon is not covered by a myelin sheath; located between internodes.
Myelin Sheath: Function
Provides electrical insulation.
Increases the speed of impulse conduction by saltatation, a method whereby the action potential jumps (or saltates) from node to node
